Plastic recycling has a new method

Today's constantly improving environmental laws and regulations, customers' environmental requirements for products, and manufacturers' requirements for the continuous recycling of plastic materials and waste have all promoted the recycling of waste plastics and related equipment. Some foreign companies have seen results in the recycling of waste plastics. In general, waste recycling can be divided into mechanical recycling, chemical recycling and raw material recycling. The mechanical recycling method is to directly discard the discarded material and make it into plastic pellets, and then send the reconstituted pellets back to the plastic manufacturing process to make a new product. The first step is to collect the plastic waste discarded by the consumer from the waste container. Through the central collection system, collected soda bottles, detergent bottles and other household wastes are collected. Together with other recyclable wastes, they are sent to the material recycling centre. The wastes and other materials are separated by machine or manpower, and various miscellaneous materials are collected. Together, the plastic wastes were sorted out. After roughly categorizing, pack it separately according to type and ship it to a plastic recycling factory.

Most of the local remanufacturers recreated transparent and colored PET, as well as primary or colored HDPE. After the remanufacturer receives the designated plastic bales from the material recovery, the compacted bales are sent to the bale breaker to be broken up into a string of loose recyclable materials, which are then fed into a dedicated shaker screen. Tiny trash and dust can fall through the screen and fall into the rubbish bin. This is the first step to remove impurities. Afterwards, the screened recyclable plastic enters the grinding and cleaning process.

First cut the material into small pieces to make the labels and other container attachments fall off. This will facilitate later cleaning. After shredding, add water to soften the debris and remove impurities, then send the debris to the washing machine. Some washers use warm water and detergents; others use room temperature water, heating the water using mechanical movements during the cleaning process. This cleaning process removes residues, dust and labels.

Then use a flotation cylinder to separate the different densities of plastic and impurities. HDPE plastic has a lower density than water and therefore floats on the water. Dust and denser plastics (such as PET) sink to the bottom of the tank and are later removed. The decontaminated cleaning debris is first blown with hot air, and then the air separator classifies the film and labels. After the plastic pieces enter the sorter, an airflow is blown down, lighter film pieces are blown away, and heavy plastic pieces continue to fall.

Finally, the plastic pieces are melted, filtered, and then pelletized by extrusion. At the beginning, the plastic chips are poured into large buckets to reduce the quality difference, and the chips are then fed into the extruder. Inside the machine is a heated cylinder with a screw conveyor inside. The chips are melted in the extruder and flow through the filter at the end of the machine. The particles of infusible impurities cannot pass through the mesh, and the pure melt squeezes through the plate drilled with small holes and becomes noodle shape. During the cooling of these plastic strips, they can be quickly cut to make pellets. Chemical recycling refers to the removal of polycondensation or addition polymerization through the depolymerization method, which changes the polymer back to monomer. Plastics that can be reconstructed in this way include polyesters (such as PET bottles for soda bottles), polyamides (such as nylon for carpets), and polyurethanes (such as foams for car seats).

For long-chain polymers, the chain can be broken chemically and thermally. If the purpose of the depolymerization is to reduce the original chemical that produced the polymer, this process is called raw material or monomer production. After decomposing the polymer into various chemical substances, the chemicals recycled as raw materials can be recovered, or various chemical substances can be used as fuel; some can also be taken as raw materials and the other can be used as fuel. Although the recycling of raw materials includes chemical recycling, it refers to the use of heat to depolymerize polyolefins and substituted polyolefins into various smaller olefin intermediates. There is not much difference between these intermediates and gasoline or lubricating oil. In some cases, heat can be used to depolymerize the addition polymer and change back directly to the monomer with a very high recovery. For example, polystyrene changes back to styrene, and polymethyl methacrylate is changed back to methyl methacrylate.

At present, there are various industrial polymerization methods that can recover recycled synthetic monomers or raw materials from plastics. There are also some methods being developed. The depolymerization process for recovering the monomer feed must be very effective. In other words, there should be a very high monomer recovery and a small amount of waste. Some plastics are particularly suitable for thermal depolymerization because of their unique chemical properties. PET and certain polyamides and polyurethanes can be depolymerized very effectively and the resulting synthetic chemicals can be used to make new plastics, without any difference from the original polymer. PET plastic bottles are the most common beverage containers, especially in developed countries, where their use is even more impressive.

Japan is one example. In 1997, the production volume of PET plastic bottles in Japan had almost reached 220,000 tons, but only one-tenth of them were recycled. As environmental protection issues have become the focus of the world, the recycling campaign has become a post-processing program that various industries must consider, prompting governments across countries to implement waste recycling programs. The Japanese government and companies are also very responsive, and the demand for PET plastic bottle recycling equipment has increased. Japan’s Tomen Group has followed the trend by introducing automatic screening machines for post-consumer plastic bottles from Austria and buying dismantling plastic bottle bales from the United States. Tomen's automatic plastic bottle screening machine is from Criterion of Binder Company and can identify eight materials such as PET, PVC, PE, PP, PS, PA and ABS. Regardless of whether the plastic bottle has a label or if the plastic bottle has been deformed, it can classify the plastic bottle at 5 to 7 per second. After the recycled PET pellets, Tomen made them into clothes.